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fast and smooth moving flame?

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Florian Fahrenbergerfast and smooth moving flame?
by on Jan 8, 2012 at 11:00:58 pm

Hey everyone!

I am quite new to Motion and absolutely amazed by its capabilities. I started using it to work on a small film project with friends and just ran into the following problem:

I want to create a torch (actually, it's supposed to be a chunk of the sun) that moves very fast in some shots.
The flame itself is not the problem, since the presets I found in the library are really helpful and I will get a satisfying result for the look I want if I tweak them a little.
However, the animation always looks crappy when the torch moves very fast, i.e. the tracked path of the particle emitter contains big steps between two frames. In those cases, the animation does not produce a smooth fire trace but a rather spotty path. Here is an example clip of what I mean (don't judge me, the flame still looks like crap...):

My first intuition would be to force Motion to animate at a higher frame rate than the underlying material. Is that possible? If my clip has 25 fps and the particle emitter rendering is done at 100 fps, it would probably already look better, right?
Can you tell me how I can achieve this easily (I have worked with Blender 3D a while ago, and for fire/smoke simulation I was able to adjust the time step of the Lattice-Boltzmann simulation seperately from the project frame rate and could therefore create "inter-frames" that only propagated the animation)? Or is there another, perhaps more elegant solution?

Greetings from Germany (pardon my English),


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Anders LarsenRe: fast and smooth moving flame?
by on Jan 9, 2012 at 11:54:31 am

Two things to try:
- Increase the Birth Rate of the flame emitter
- Render with Motion Blur turned on. (And the number of samples as high as you have patience for)

Does that help?

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Florian FahrenbergerRe: fast and smooth moving flame?
by on Jan 9, 2012 at 7:12:32 pm

Increasing the birth rate does nothing, it only increases the amount of particles created per frame, they still are created only once per frame and leave a spotty path.

Motion blur helps to some extent, but still far from ideal.

Any more ideas?

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Stephen SmithRe: fast and smooth moving flame?
by on Jan 9, 2012 at 7:32:15 pm

If someone has a solution to this I would love to know what it is. What I've done to get around this is export out the fire all by itself so it becomes a self-contained movie. Then track the fire movie instead of a particle.

Stephen Smith
Utah Video Productions

Check out my Motion Training DVD

Check out my Vimeo page

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Florian FahrenbergerRe: fast and smooth moving flame?
by on Jan 9, 2012 at 8:07:26 pm

By now I have found kind of a workaround myself. To get more timesteps for the animation, I simply slowed down the background footage (say to 25%), did the tracking and put in the fire. Then I discarded the background footage, sped up the fire animation to the according 400% and put the original footage in the back for composition.

Not the most elegant or fast way, but it worked for me to get 4 times the amount of simulated frames compared to the original, where only every fourth is written out in the end. It was enough for me to get a smooth track when applying motion blur in addition.

If I find a better way, I will report back.

Greetings from Germany,


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